1. FIELD OF THE INVENTION
The invention relates to a method and apparatus for providing a "pre-packed" gravel packing screen for use in subterranean oil and gas wells.
2. SUMMARY OF THE PRIOR ART
When oil and gas wells are drilled through formations which generally are of an unconsolidated nature, the produced fluids can be expected to contain particulate, solid matter, generally referred to as "sand". It is undesirable to produce such particulate matter with the production fluids because of abrasion of production tubing, valves and other equipment used to produce the well and carry such fluids from the well, through the sales line, and the like. It is therefore necessary in such instances to avoid production of such sand and other particulate matter with the fluids.
In the past, those skilled in the art have reduced the production of sand by "gravel packing" the well during the completion operation. Such gravel packing has included providing on the production conduit or tubular work string a device including a slotted or ported cylindrically shaped member which prevents the passage therethrough and into the interior of the conduit of solid particles exceeding a predetermined size. Such devices are incorporated into equipment and methods wherein gravel is introduced into the annular area between the production conduit or work string and the casing of the well (or, in the event of non-cased wells, the well bore wall), with the gravel being deposited longitudinally exteriorly of the slotted or ported cylindrical member.
Gravel packing of such wells has also been effected by means of incorporation onto the production or work string of a "pre-pack" apparatus, wherein gravel, glass beads, or other solid particulate is disposed in between an outer member, such as stainless steel wire wrapped screen, and an inner ported member, such that the device may be carried into the well and positioned adjacent the production zone to thereby prevent the particulate sand produced with the production fluids from entering the interior of the conduit and being produced to the top of the well with the production fluids. Such "pre-packs" may be used alone or in conjunction with apparatus and method wherein the well bore is also gravel packed.
The present invention provides a "pre-packed" apparatus and method for gravel packing a subterranean oil or gas well wherein a wire mesh having selective sized openings between the mesh members is provided in the apparatus, instead of incorporation of the solid particulate materials used in the prior art.
The prior art contains a number of references of gravel packing methods and apparatuses incorporating slotted, ported or wire-wrapped screen devices which have disposed therein particulate matter, such as glass beads, gravel, and the like, including the following U.S. Pat. Nos.:
______________________________________ U.S. Pat. No. Title ______________________________________ 1,218,848 STRAINER FOR PUMPS 2,190,989 METHOD OF PREPARING AN OIL WELL FOR PRODUCTION 2,371,385 GRAVEL PACKED LINER AND PERFORA- TION ASSEMBLY 2,523,091 OIL-WATER SEPARATOR FOR WELLS 2,525,897 WELL PIPE FILTER 2,530,223 OIL WELL FILTER 2,877,852 WELL FILTERS 2,978,033 DRILLABLE PREPACKED SAND CONTROL LINER 2,981,332 WELL SCREENING METHOD AND DEVICE THEREFOR 3,261,401 WATER PRODUCTION 3,455,387 WELL COMPLETION TECHNIQUE AND APPARATUS FOR USE THEREWITH 4,494,603 WIRE MESH WELL SCREEN WITH WELDED WIRE SUPPORT 4,583,594 DOUBLE WALLED SCREEN-FILTER WITH PERFORATED JOINTS 4,526,230 DOUBLE WALLED SCREEN-FILTER WITH PERFORATED JOINTS 4,649,996 DOUBLE WALLED SCREEN-FILTER WITH PERFORATED JOINTS ______________________________________
Representative of the prior art is U.S. Pat. No. 4,494,603, which includes an outer stainless steel wire wrapped screen, such as shown in FIGS. 1 and 3 thereof, disposed around a series of circumferentially extending porous rod elements 12. Such screen would not be desirable for use in subterranean oil and gas wells, contemplated herein, and particularly in conjunction with method and apparatus for completing non-vertical wells, also as contemplated herein, with such device including wire mesh disposed between the support rods and the helically wrapped wires. There are many reasons why such construction is inappropriate for use in completion techniques for subterranean oil and gas wells, although such device may have some application in shallow, water wells. For example, such device, incorporating the rods, cannot provide the tensile load through the rods to carry sections of production and work string therebelow, as is often customary in completion techniques for subterranean oil and gas wells completed at extensive depths.
For many years the desirability of utilizing a subterranean well bore having a non-vertical or horizontal portion traversing a production formation has been known and appreciated in the prior art. Laterally directed bores are drilled radially, usually horizontally, from the primary vertical well bore, in order to increase contact with the production formation. Most production formations have a substantial horizontal extent and, when conventional vertical well bores are employed to tap such production formations, a large number of vertical bores must be employed. With the drilling of a well bore having a non-vertical or horizontal portion traversing the production formation, a much greater area of the production formation may be traversed by the well bore and the total field drilling costs may be substantially decreased. Additionally, after a particular horizontal well bore has produced all of the economically available hydrocarbons, the same vertical well bore may be redrilled to establish another horizontal portion extending in another direction and thus prolong the utility of the vertical portion of the well and increase the productivity of the well to include the total production formation.
One of the completion techniques that has not been worked out, particularly for wells having medium radius turns on the order of about 10.degree.-90.degree. per 100 feet of well length, is the design, insertion and operation of gravel packing or other Sand Control equipment. Wells incorporating such medium radius curvature between the horizontal and vertical portions of the well bore have been completed only by utilizing the open hole technique or inserting a slotted liner.
U.S. Pat. No. 4,553,595 to HUANG et al proposed that gravel packing be accomplished in two distinct steps. In the first step, the horizontal segment of the well bore is provided with a foundation layer of unconsolidated gravel supplied through a flexible tube, hence with no control of the depth of the layer. A perforated liner is then introduced into the well resting on the initial layer of gravel. Those skilled in the art will recognize that "gravel" used in gravel packing of a well, as well as the material referred to herein in "pre-packed" screens, can be coarse sand, glass beads, solid polymeric-like substances, and the like, and can generally be defined as solid particulate matter which blocks the entry into the production tubing of produced sand and other solids but permits the flow into the production tubing of the production fluids.
The second phase of the gravel pack is achieved by introducing a gravel slurry through flexible hoses attached to the exterior of the slotted liner, such slurry being deposited on the foundation bed and hopefully building up around the liner. The disadvantages and shortcomings of this approach will be readily apparent to those skilled in the art.
Gravel packing of conventional wells is efficiently accomplished by gravel packing apparatus of the type disclosed in U.S. Pat. No. 3,987,854 to CALLIHAN et al. The apparatus employed in this patent incorporates a hydraulically operated packer, which is connected to the top of a screen section. The packer is provided with conventional left hand threads which in turn are connected to a left hand threaded nut carried on the top end of a cross-over tool which is secured to the bottom end of a tubing string.
This conventional type of gravel packing apparatus is unsuited for the gravel packing of horizontal well bores having a significant longitudinal extent on the order of 1000-2000 feet, and more. In the first place, to insert this apparatus through the radius portion of the well bore, it may be necessary that the apparatus be rotated, which rotation will of course be in a clockwise direction, as is conventional. The resistance to passage of the apparatus through the short radius curved sections of the well bore is sufficiently high as to allow clockwise rotation of the left hand threaded nut relative to the packer. Thus, the packer and nut would become disengaged upon the application of excessive torques required to rotationally insert the gravel packing tool into the well.
An even more important deficiency lies in the fact that the introduction of the gravel packing fluid is conventionally accomplished by flowing the gravel containing fluid externally through the annulus defined between the screens and the well bore. With a well bore having a non-vertical, and particularly a horizontal extent of 1000 to about 2000 feet, there is no assurance that the gravel contained in the gravel packing fluid will not build up around centralizers and bridge across the annulus long before it reaches the end of the 1000-2000 foot length of screen traversing the horizontal production formation.
Any attempt to utilize conventional centralizers to center the multitude of screens relative to the horizontal well bore also creates additional problems. All conventional centralizers are subject to destruction by rotation of the tubing string upon which they are carried, particularly when compressed betweeen the wall of the well bore or casing and the tool string. Thus, the employment of conventional stabilizers, which are essential for locating the screens axially aligned within the well bore, is effectively prohibited by the required rotation of the screens during the process of inserting the tool string through any radius curved portion of the well bore. These are only a few of the problems that must be solved if the industry goal of achieving efficient production from well bores having non-vertical or horizontal portions of substantial longitudinal extent traversing production formations, is to be accomplished.